1. Field of the Invention
The invention relates generally to the art of axle/suspension systems for heavy-duty vehicles. More particularly, the invention relates to axle/suspension systems for heavy-duty vehicles, which utilize an air spring or other cushioning means that operates in more than a single plane to cushion the ride of the vehicle. More specifically, the invention is directed to a directional damper for a heavy-duty vehicle axle/suspension system, whereby the directional damper is capable of managing or controlling the direction of damping of the axle/suspension system with respect to a predetermined datum, and that results in optimized damping of the axle/suspension system during operation of the heavy-duty vehicle and improved ride quality for the heavy-duty vehicle.
2. Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members, which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger, which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The beam end opposite the pivotal connection end also is connected to an air spring, or other spring mechanism, which in turn is connected to a respective one of the main members. A height control valve is mounted on the main member or other support structure and is operatively connected to the beam and to the air spring in order to maintain the ride height of the vehicle. A brake system and, optionally, one or more shock absorbers for providing damping to the axle/suspension system of the vehicle also are mounted on the axle/suspension system. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react and/or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle as well as certain road conditions, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to have beams that are fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system. It is also desirable to dampen the vibrations or oscillations that result from such forces. A key component of the axle/suspension system that cushions the ride of the vehicle from vertical impacts is the air spring, while a shock absorber typically provides damping characteristics to the axle/suspension system.
The typical air spring of the type utilized in heavy-duty air-ride axle/suspension systems includes three main components, a flexible bellows, a piston and a bellows top plate. The bellows is typically formed from rubber or other flexible material, and is operatively mounted on top of the piston. The piston is typically formed from steel, aluminum, fiber reinforced plastics or other rigid material, and is mounted on the rear end of the top plate of the beam of the suspension assembly by fasteners of the type that are generally well known in the art. The volume of pressurized air, or “air volume”, that is contained within the air spring is a major factor in determining the spring rate of the air spring. More specifically, this air volume is contained within the bellows and, in some cases, the piston of the air spring. The larger the air volume of the air spring, the lower the spring rate of the air spring. A lower spring rate is generally more desirable in the heavy-duty vehicle industry because it provides a softer ride to the vehicle during operation. Typically, the piston either contains a hollow cavity, which is in communication with the bellows and which adds to the air volume of the air spring by allowing unrestricted communication of air between the piston and the bellows volumes, or the piston has a generally hollow cylindrical-shape and does not communicate with the bellows volume, whereby the piston does not contribute to the air volume of the air spring. The air volume of the air spring is in fluid communication with the height control valve of the vehicle, which in turn is in fluid communication with an air source, such as an air supply tank. The height control valve, by directing air flow into and out of the air spring of the axle/suspension system, helps maintain the desired ride height of the vehicle.
Prior art air springs such as the ones described above, while providing cushioning to the vehicle cargo and occupant(s) during operation of the vehicle, provide little if any damping characteristics to the axle/suspension system. Such damping characteristics are instead typically provided by a pair of hydraulic shock absorbers, although a single shock absorber has also been utilized and is generally well known in the art, as is the use of a plurality of shock absorbers in extra heavy-duty applications. Each one of the shock absorbers is mounted on and extends between the beam of a respective one of the suspension assemblies of the axle/suspension system and a respective one of the main members of the vehicle or to another structure that connects to the main member.
More particularly, a pair of prior art shock absorbers of the type utilized in heavy-duty air-ride axle/suspension systems generally include a cylinder and a piston rod reciprocating within the cylinder. The cylinder is filled with an operating fluid, such as gas or oil, such that the operating fluid is moved by a piston valve secured to one end of the piston rod to generate a damping force.
As set forth above, each one of the prior art shock absorbers is mounted on and extends between the beam of a respective one of the suspension assemblies of the axle/suspension system and a respective one of the main members of the vehicle or other component fixed to the main member, such as the hanger. More particularly, the upper end of the shock absorber is fastened to a clevis-type bracket that is mounted on a wing that extends inboardly from the hanger. The lower end of the shock absorber is rigidly fastened to a mount that extends from the inboard sidewall of the beam of the suspension assembly.
Because prior art shock absorbers are rigidly fastened to mounts that are attached to the vehicle frame and the beam resulting in an angled orientation, these prior art shock absorbers can create fore-aft forces or loads that are transmitted into the suspension assembly of the axle/suspension system during operation of the vehicle and, therefore, do not provide optimal damping to the axle/suspension system. More specifically, the position of the shock absorber on the suspension assembly does not provide optimal damping to the axle/suspension system during operation of the vehicle because the angle of the damping inputs from the shock absorber to the beam and the vehicle frame are not perpendicular to the beam as it rotates. This creates the aforementioned fore-aft loading on the beam of the suspension assembly, which in turn can potentially reduce the effectiveness of the components of the axle/suspension system and/or the shock absorbers. The directional damper of the present invention overcomes the problems associated with the prior art damping shock absorbers, by providing a directional damper that is capable of managing or controlling the overall direction of damping of the axle/suspension system relative to a predetermined datum, and that results in optimized damping of the axle/suspension system during operation of the heavy-duty vehicle, in turn resulting in improved ride quality for the heavy-duty vehicle.